Heat sinks have been widely used to assist in cooling electronic components. Some microprocessors have heat sinks attached to allow for higher-frequency operation. Other components such as memory modules may also benefit from heat sinks.
Most personal computers (PC's) are shipped with sockets for memory modules so that their owners can later add additional modules, increasing the memory capacity of the PC. Other non-PC devices may also use memory modules designed for PC's. High-volume production and competition have driven module costs down dramatically, benefiting the buyer.
Memory modules are made in many different sizes and capacities, with the older 30-pin modules replaced by 72-pin, 168-pin, and other size modules. The “pins” were originally pins extending from the module's edge, but now most modules are lead-free, having metal contact pads, fingers, or leads. The modules are small in size, some being about 5.25 inches long and 1.2 or 1.7-inches high.
Conventional memory modules include a small printed-circuit board (PCB) substrate and several surface mounted components (e.g., memory devices) mounted on one or both surfaces of the PCB substrate. The PCB substrate is typically a multi-layer board with alternating laminated layers of fiberglass insulation and foil or metal interconnection layers. The contact pads (or other contact structures) are typically aligned along a bottom (connector) edge of the PCB substrate. The interconnect layers define wiring traces that provide signal paths between the surface mounted components and the contact pads. The surface mounted components (e.g., memory devices) are soldered or otherwise attached to one or both surfaces of the substrate, with each component typically including one or more integrated circuit (IC) “chips” that are packaged in inexpensive surface-mount packages such as small-outline J-leaded (SOJ) packages, plastic leaded chip carriers (PLCC's), thin small-outline packages (TSOP) or small-outline (SO) packages. The number of memory devices mounted on the PCB substrate of a memory module depends on the capacity and the data-width of the memory chips and the size of the memory module.
FIG. 13 is a diagram showing a memory module with dynamic-random-access memory (DRAM) devices. The memory module contains substrate 10, with surface-mounted DRAM devices 20 mounted directly to the front surface or side of substrate 10, while more DRAM devices (not visible) are usually mounted to the back side or surface of substrate 10. Metal contact pads 12 are positioned along the bottom or connector edge of the module on both front and back surfaces. When the memory module is mounted into a host system (e.g., a personal computer (PC)), metal contact pads 12 mate with pads on a module socket (not shown) to electrically connect the module to the host system's motherboard. Holes and/or notches 14, 16 are sometimes used to ensure that the module is correctly positioned in the socket. For example, notch 14 can be offset from the center of substrate 10 to ensure that the memory module cannot be inserted backwards in a socket. Notches 16 match with clamps of the module socket to ensure that the memory module is securely positioned in the socket.
As processor speeds have increased, the need for faster memory has become more critical. Various bandwidth-enhancing methods and memory interfaces have been used. Memory chips have higher densities and operate at higher frequencies than before, producing more waste heat from the memory chips. Thus, a need has arisen to remove this waste heat from memory modules.
Conventional memory module assemblies typically include three components: the memory module PCBA and two metal heat-sink plates that are coupled together using one or more fasteners, such as a metal clamp. The contact between PCBA and metal heat-sink plate is usually aided by sandwiching a tape of thermal interface material (TIM) in-between. Various heat-sink plates have been designed for producing such memory module assemblies. See for example U.S. Pat. Nos. 6,362,966, 6,424,532, and 6,449,156, among others. Clamp-on heat-sink plates for memory modules are also known. For example, OCZ Technology produces a copper heat sink with wider metal bands that clip the heat sink to over the front and back surfaces of the memory module. These clip-on and clamp-on designs increase the manufacturing costs and complexity of the associated memory modules because they are difficult to incorporate into automated production lines. Further, the use of clamps or similar structures facilitates easy disassembly by users, resulting in undesirable situations. Moreover, the presence of the clamps and thermal interface material increase the overall thickness of the memory module assembly, thereby taking up valuable motherboard space.
Some memory-module heat sinks feature a closed-top design that prevents airflow in the small gaps between the heat sink and the memory module substrate. Often the entire top edge of the heat sink is closed, providing no path for air to flow under the heat sink other than back out the bottom edge, which is usually open. Sides may be open or partially open, but the sides are much smaller than the top and bottom edges of the memory module, limiting the possible air-flow.
What is needed is a memory module assembly having a protective metal heat-sink plate (shield) mounted over the surface mounted IC devices of a memory module PCBA that both serves to protect the PCBA and to dissipate heat generated by the IC devices, and is easily and inexpensively produced using automated methods.